1. Technical Field
This invention relates to the field of apparatus for forming pressed paperboard products such as paper trays and plates.
2. Description of Related Art
Paperboard products, such as trays and plates, are formed, generally, by a method of molding fibers from a pulp slurry into the desired form of the product or by pressing a paperboard blank between forming dies into the desired shape. Manufacturing of paper products by the press forming process provides a number of advantages typically not found in products produced by other methods, such as the molded pulp process. Pressed paperboard products can be decorated and coated with a liquid-proof coating before being stamped by the forming dies into the desired shape whereas pulp molding processes permit the coating and decoration steps to occur only during or after the molding step. Coating and decorating a non-planar surface normally tends to be more expensive and difficult. Further, pressed paperboard products generally cost less, and require less storage space and can sometimes be transported in a collapsed condition, unlike molded pulp articles. Because press formed paperboard products can be manufactured more cost effectively than molded pulp articles and can be provided with features which improve product functionality and use, the press forming process is practiced by a substantial number of manufacturers in the paper product industry.
In press forming paperboard products, the apparatus which is typically utilized comprises, generally, a supply of paperboard in the form of a web on a reel, a blank and scoring section for cutting and scoring blanks having desired dimensions and a forming section including a die set for receiving blanks and press forming the blanks to form a finished paperboard product of the desired size and shape, such as is disclosed in U S. Pat. No. 4,609,140 to Van Handel et al and U.S. Pat. No. 4,606,496 to Marx, et. al. In most cases, a pre-printed pattern is disposed on the surface of the paperboard web, such that blanking must occur in proper registration with the feeding of the web. Further, in an apparatus of this type, both the blanking and forming sections are cyclically operated and the blanking and forming operations (i.e., cycles) must be accurately synchronized in order to ensure that each blank is accurately positioned at the appropriate time in the die cavity of the forming section's die set. The timing and proper placement of the blank in the die cavity is crucial to the formation of a sufficiently rigid and well-defined paperboard product having the desired shape, such as is desirable by the ultimate consumer.
The typical press forming apparatus, such as is described above, while being suitable for producing a satisfactory press formed product having the desired rigidity and shape characteristics, does not operate with maximum efficiency (i.e., the number of products produced on a per cycle basis), and further, is substantially limited with respect to output capacity (i.e., the number of products produced per minute). In operation of the above described apparatus, a single blank is cut and a single press formed product is produced per forming section cycle. Therefore, to increase efficiency the number of products produced per cycle must be increased and to increase output capacity the rate at which the blanking and forming sections operate must be increased. Increasing the number of products produced per forming cycle is, however, extremely limited in that only a single die cavity for receiving blanks is provided. Further, the number of products produced per minute is limited by the maximum number of cycles per minute at which the blanking and/or forming sections may be operated. The maximum cycle rate of blanking apparatus is approximately 80 to 150 cycles per minute, while the maximum cycle rate of forming apparatus is approximately 40 to 50 cycle per minute. Operation in excess of these maximum cycle rates would result in considerable registration problems, with respect to the blanking operation. Such high speed operation can also lead to a significant breakdown in synchronization between the blanking and forming sections, thereby causing blanking out of registry and positioning improperly of blanks in the forming section. Lack of synchronization may also cause the finished products to have incorrect patterning, distorted shapes, imprecise pleat formation and insufficient rigidity characteristics. Manufacturers of pressed paper products would be in a better position to capitalize on their inherent lower manufacturing costs if press forming apparatus could be designed to operate more efficiently with increased output capacity, increasing the number of products press formed per cycle and produced per minute, while still consistently forming finished products having the desired pattern, shape and rigidity characteristics.
One typically utilized method for increasing productivity by increasing the number of products produced per minute is to operate a plurality of parallel process lines of press forming apparatus. While increasing overall manufacturing productivity, this alternative is very costly and is limited by the availability of manufacturing floor space (i.e., because the apparatus are placed side by side). There is a need for an alternative method and accompanying apparatus, which can increase productivity by increasing the number of products produced per cycle and per minute by each press forming apparatus, operating individually or in a parallel processing line environment.
Many attempts have been made to overcome the limitations on efficiency and output capacity of the typical press forming apparatus. A known method and apparatus for press forming paperboard products with increased efficiency and output capacity is to feed multiple blanks into a single die cavity for each cycle of the forming section. This method of operation and accompanying apparatus, as shown for example in U.S. Pat. No. 4,242,293 to Dowd, results in a substantial increase in the number of press formed products produced per cycle and per minute, limited only by the maximum number of blanks which may be placed in the single die cavity during each forming cycle and the maximum cycle rate of the blanking section. While increasing efficiency and output capacity, press forming multiple blanks in a single die cavity results, generally, in the formation of a paperboard product of a very poor quality, unsuitable both functionally and aesthetically for many of the end uses contemplated by the ultimate consumer. As a result of the stacking of multiple blanks in a single die cavity, the compressive forces exerted on each of the blanks will be different. It is crucial that the compressive forces exerted on each blank be sufficient to cause the occurrence of fiber bonding in order to impart the finished product with sufficient rigidity to withstand the stresses of normal everyday use by the ultimate consumer. In addition, the positioning of each blank relative to the upper and lower forming surfaces of the die plates will also be different. It is very important to and expected by the ultimate consumer that each finished paperboard product consistently have the same well-defined shape. In view of the foregoing, the multiple blank per cavity press forming method and apparatus cannot consistently produce sufficiently rigid and well-defined shaped paperboard products as is clearly desirable by both the manufacturer and the ultimate consumer.
Other attempts at increasing efficiency and output capacity of press forming apparatus are characterized by providing a forming section (i.e., die set) having multiple die cavities, thereby increasing the number of products produced per forming cycle. In particular, a press forming apparatus is provided including a first web for feeding a first cavity of a dual cavity die set and a second web for feeding a second cavity of the dual cavity die set, such as is disclosed in U.S. Pat. Nos. 4,636,348 to Whiteside and U.S. Pat. No. 4,427,476 to Beck et al. The patents to Whiteside and Beck et al., although being directed to the press formation of thermoplastic materials and the like, do disclose press forming apparatus having the capability to increase the number of products produced per forming cycle. However, increasing efficiency and output capacity by the provision of a different web for feeding each die cavity of a dual cavity die set would not be acceptable with respect to a paperboard web and the products press formed therefrom, in view of the substantial increase in manufacturing costs, as a result of the purchase price, maintenance and operating expenses associated with each additional web feeding mechanism, registration system and blanking apparatus, as well as, the significant additional manufacturing floor space that would be required.
Notwithstanding the known apparatus for increasing efficiency and output capacity for the press forming of paperboard products, there is a need for a press forming method and apparatus which can operate efficiently, by increasing the number of products produced per cycle, with an increased output capacity, by increasing the number of products produced per minute, while not requiring a substantial increase in manufacturing costs or floor space and consistently producing finished products having superior shape definition, rigidity and patterning characteristics.